1. Field of the Invention
The present invention relates to a method of making a duct from a flat board utilizing a grip flange. In particular, the board from which the duct is made is a rigid or a semi-rigid material capable of undergoing at least a small amount of compressive deformation and the grip flange is mounted to the board for assembly of the duct without the utilization of adhesives or welding.
2. Prior Art
A board having these qualities has recently been produced for use in forming thermally insulating ducts such as are employed for heating, ventilation and air conditioning. It consists of a rigid foamed plastics material, for example, a closed cell expanded phenolic foam, although other open or closed cell expanded foam materials such as polyurethanes could be used. As produced, the expanded plastics material is in the form of a planar board having a metallic foil, for example of aluminum, bonded to each major surface. Ducting, typically of rectangular cross section, may be produced therefrom.
As opposed to conventional ducts formed of metal sheet, the product is light, with good thermal insulating properties, and often sufficiently rigid per se for the intended use (although further strengthening measures can be taken in this respect if necessary, for example when requiring long unsupported spans, large cross-sectional areas, or significant differential pressures between interior and exterior). However, a problem arises as to how to firmly and efficiently couple together edge portions of the planar board to form ducting of a polygonal cross-section and how to couple a length of duct so formed either to a further length thereof, or to ancillary equipment such as a fan.